text: In chemistry, a regular solution is a solution whose entropy of mixing is equal to that of an ideal solution with the same composition, but is non-ideal due to a nonzero enthalpy of mixing. Such a solution is formed by random mixing of components of similar molar volume and without strong specific interactions, and its behavior diverges from that of an ideal solution by showing phase separation at intermediate compositions and temperatures (a miscibility gap). Its entropy of mixing is equal to that of an ideal solution with the same composition, due to random mixing without strong specific interactions. For two components 
  where  is the gas constant,  the total number of moles, and  the mole fraction of each component. Only the enthalpy of mixing is non-zero, unlike for an ideal solution, while the volume of the solution equals the sum of volumes of components.